There are known an engine method (Fuel for engines. An engine method for determining of octane rating. The USSR State Standard 511-82, ASTM D 2700, DIN 51756) and an analyze method (Fuel for engines. An analyze method for determining of octane rating. The USSR State Standard 8226-82, ASTM D 2699, DIN 51756) for determining of the knock rating of fuels including feeding the fuel into a reaction vessel with variable degree of compression, atomization and ignition of a mixture, determining the knock rating. The method is performed on a one-cylinder engine having variable degree of compression, and the knock rating is expressed by octane rating numerically equal to percentage of isooctane in such a mixture with normal heptane, knock intensity of which in a one-cylinder engine having variable degree of compression in standard conditions of testing is equivalent to knock intensity of the tested fuel.
The methods based on engine tests correctly, in general, characterize fuels, but exhibit significant drawbacks. Those drawbacks include considerable duration of testing and large consumption of tested fuel. So, testing of one sample of fuel using the engine or research methods lasts for 20 minutes and consumes a tested sample of 300 ml. Intense exhaust into atmosphere of harmful products of combustion is one of negative consequences of the large fuel consumption. Because of large consumption of the sample, these methods practically cannot be used for testing of products, obtained on micro-pilot plants.
Besides, it is very difficult to include these methods into a technological scheme for on-stream testing of the products or to use them in a system of automatic control. Furthermore, engines used in the mentioned methods are quite expensive and cumbersome.
The closest on technical essence and achieved result is a method based on initiation of low temperature reaction of gaseous phase oxidation of fuel. The method provides thermostatic control of the reaction vessel of constant volume up to temperatures 250-350.degree. C., feeding of a portion of tested fuel, mixing it with air contained in the vessel at atmospheric pressure, cool flame oxidation of the formed combustible mixture. Temperature in the reaction vessel increases. The knock rating of motor fuel is characterized by temperature gain and time of achieving of maximal temperature. With deterioration of the knock rating of a sample, the temperature is increased, and the time of achieving of maximal temperature is reduced (U.S. Pat. No. 3,738,810, G01L 23/22, 1973).
Methods and devices based on studying of cool flame processes have number of advantages: they are rather inexpensive, application thereof requires insignificant amount of a sample, they could be easily included into a technological system for on-stream testing of products, and they could also be used in a system of automatic control. They possess, however, one quite essential drawback; testing of fuel is performed in conditions rather far from engine operational conditions. Knocking occurs in an engine during combustion of fuel, but in the considered method combustion does not occur at all. Using this method there could be studied phenomena occurring to fuel during preparation for combustion, pre-combustion processes. The distinction between conditions of fuel combustion in an engine and its testing in conditions of cool flame oxidation limits possibilities of the given testing method. The mentioned method gives satisfactory results at testing of homogeneous fuels samples of known composition with insignificant changes, for example, at the output of the technological system. If fuel composition is unknown, the results of testing may be unreliable. Besides, employing of this method, it is practically impossible to estimate efficiency of antiknock additions, since the mechanism of their action is absolutely different, and it is impossible to judge their efficiency using cool flame processes. Therefore, the given method is recommended to use for the control of mixing processes, in which there are not applied antiknock additions, in particular, tetraethyl lead (Clinton R. M., Puzniak T. J. Gulf Research develops continuous-process octane analyzer. Oil and Gas Journal, 1975, 73, No. 16, 77-82).